JP2009204650A - Image display apparatus using laser light source and image display method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for reducing effect of a speckle pattern to a display image in an image display apparatus using a laser light source. <P>SOLUTION: This image display apparatus using the laser light source includes a light modulating part for modulating a laser beam emitted from the laser light source to image light representing a frame image, and a light modulation signal generating part for generating a light modulation signal for driving the light modulating part according to an image signal for updating the frame image in a fixed cycle. The light modulation signal generating part inserts noise in the light modulation signal while the timing of updating the frame image is kept in a fixed cycle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image display device using a laser light source.

  An image display device is known that modulates laser light emitted from a light source device based on an image signal and projects the modulated laser light on a display screen such as a screen (Patent Document 1 or the like).

Japanese Patent Laid-Open No. 6-208089

  However, in such an image display device, when laser light is scattered by an optical element provided on the optical path, the coherence of the laser light is high, so that a random interference pattern (speckle pattern) is displayed on the display image. ) May appear. When the speckle pattern occurs, the viewer of the display image feels flickering in the display image and recognizes that the display image is unclear. Until now, it was the actual situation that sufficient ideas were not made to such a problem.

  An object of the present invention is to provide a technique capable of reducing the influence of speckle patterns on a display image in an image display device using a laser light source.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 An image display apparatus using a laser light source,
A light modulation unit that modulates laser light emitted from the laser light source into image light representing an image;
A drive signal generation unit that generates a drive signal for driving the light modulation unit based on an image signal of a frame image updated at a constant first period;
With
The image display device, wherein the drive signal generation unit periodically inserts a noise image into the drive signal while maintaining a timing at which display of the frame image is updated in the first cycle.
According to the image display device described in Application Example 1, the complex amplitude on the display screen can be changed by displaying the noise image inserted in the drive signal on the display screen. Therefore, even when a speckle pattern is generated by the laser light source, the influence of the speckle pattern on the display image can be reduced by the variation of the complex amplitude.

Application Example 2 An image display device according to Application Example 1,
The noise image periodically inserted is an image display device that is a random noise image that becomes a uniform image in which a specific pattern does not appear when a plurality of noise images are integrated in a time direction.
According to the image display device described in the application example 2, it is possible to suppress the observer of the display image from recognizing the noise pattern inserted in the display image.

[Application Example 3] The image display device according to Application Example 1 or Application Example 2,
The drive signal generation unit generates a frame image drive signal for displaying the frame image as a non-noise frame image not including the noise image in the first period,
An image display device that generates a noise image drive signal for displaying the noise image at a constant second period.
According to the image display device described in the application example 3, the frame image representing the moving image is displayed with the constant first period, and the noise image is inserted and displayed between the frame images with the constant second period. The Therefore, in a cycle (second cycle) in which the observer of the display image can suppress the recognition of the noise image while displaying the frame image in a cycle (first cycle) in which the viewer of the display image can recognize the moving image. A noise frame image can be displayed. Thereby, the influence of the speckle pattern on the display image can be reduced, and the observer of the display image can be prevented from recognizing the noise pattern inserted in the display image.

Application Example 4 The image display device according to Application Example 3,
The drive signal generation unit further generates a predicted frame image predicted as an intermediate image between each pair of frame images arranged in chronological order as a non-noise frame image not including the noise image, and the predicted frame image An image display device that generates a predicted frame image drive signal for displaying the image at the first period.
According to the image display device described in the application example 4, the insertion of the predicted frame image allows the viewer of the display image to feel the motion represented by the moving image more smoothly.

Application Example 5 An image display device according to Application Example 3 or Application Example 4,
The image display device, wherein the second period is equal to the first period.
According to the image display device described in application example 5, it is possible to more effectively reduce the influence of the speckle pattern on the display image.

Application Example 6 The image display device according to any one of Application Example 3 to Application Example 5,
The image display device, wherein the average luminance level of the noise image is set in conjunction with an average luminance level of a predetermined number of the non-noise frame images displayed before the noise image.
According to the image display device described in the application example 6, it is possible to prevent the average luminance level of the non-noise frame image from being significantly different from the average luminance level of the noise image displayed following the non-noise frame image. it can. Therefore, it is possible to suppress the observer of the display image from recognizing the influence on the average luminance level of the display image due to the insertion of the noise image.

Application Example 7 The image display device according to any one of Application Example 1 to Application Example 6,
When the noise image is Fourier-transformed, the amplitude intensity of the first frequency band whose frequency is near 0 is lower than the amplitude intensity of the second frequency band on the higher frequency side than the first frequency band. An image display device that is an image.
According to the image display device described in the application example 7, since the noise image including more high-frequency components than the low-frequency components is inserted, the complex amplitude on the focal plane of the laser light can be changed more greatly. Therefore, the influence on the display image by the speckle pattern can be further reduced.

Application Example 8 The image display device according to any one of Application Example 1 to Application Example 7,
An image display device in which the noise images displayed within at least one second are all different.
According to the image display device described in application example 8, it is possible to further suppress the recognition of the noise image inserted by the observer of the display image.

[Application Example 9] The image display device according to Application Example 1 or Application Example 2,
The drive signal generator is
An image display device that generates a frame image drive signal with noise for displaying a frame image with noise obtained by synthesizing the noise image with the frame image at the first period.
According to the image display device described in the application example 9, since the noise image is displayed together with the frame image, it is possible to reduce the influence of the speckle pattern on the display image while displaying the frame image. Further, the frame period can be made smaller than when the noise image and the frame image are displayed alternately.

Application Example 10 The image display device according to Application Example 9,
The drive signal generation unit further includes
Generating a predicted frame image that is predicted as an intermediate image between each pair of frame images arranged in chronological order;
While generating a prediction frame image with noise obtained by synthesizing the noise image with the prediction frame image,
The image display apparatus which produces | generates the prediction frame image drive signal with a noise for displaying the said prediction frame image with a noise with a said 1st period.
According to the image display device described in the application example 10, it is possible to make the motion represented by the moving image more smoothly perceived by the observer of the display image by generating the noise-predicted frame, and to the display image by the speckle pattern. The influence can also be reduced.

  The present invention can be realized in various forms. For example, an image display method and an image display device using a laser light source, a control method for the image display device, a control device for the image display device, and those methods Alternatively, the present invention can be realized in the form of a computer program for realizing the functions of the apparatus, a recording medium on which the computer program is recorded, or the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Fourth embodiment:
E. Example 5:
F. Example 6:
G. Variations:

A. First embodiment:
FIG. 1 is a schematic diagram showing a configuration of an image display apparatus 100 as an embodiment of the present invention. The image display apparatus 100 is a projection display apparatus that displays a color image by projecting image light modulated in accordance with an image signal representing an image onto a projection screen 200.

  The image display device 100 includes three image light emitting devices 10R, 10G, and 10B, a cross dichroic prism 20, and a projection lens 30. The three image light emitting devices 10R, 10G, and 10B emit image light for each of the three color components of red, green, and blue. Here, “image light” means light representing an image in which light from a light source is modulated based on an image signal described later. The image light of each color component emitted from each of the image light emitting devices 10R, 10G, and 10B is incident on the incident surfaces 21R, 21G, and 21B of the cross dichroic prism 20. The image light of each color component is synthesized by the cross dichroic prism 20 and is emitted from the emission surface 22. The combined image light is magnified by the projection lens 30 and projected onto the projection screen 200.

  FIG. 2A is a schematic diagram illustrating a configuration of a red component image light emitting device 10R that emits red component image light. FIG. 2B is a perspective view corresponding to FIG. Since the other color component image light emitting devices 10G and 10B have the same configuration as the red component image light emitting device 10R, illustration and description thereof are omitted. The red component image light emitting device 10R includes a laser array light source device 1R that emits red laser light, a diffractive optical element 2, a field lens 3, and a liquid crystal panel 4R for red component light. The laser array light source device 1R emits a plurality of parallel red laser beams Lr1 arranged at equal intervals toward the diffractive optical element 2. The diffractive optical element 2 emits diffracted light Lr2 obtained by diffusing each laser beam Lr1. The diffracted light Lr2 enters the lens surface of the field lens 3, is refracted by the field lens 3, and illuminates a predetermined illumination region (described later) of the liquid crystal panel 4R for red component light in a superimposed and uniform manner.

  FIG. 3 is a schematic diagram showing the configuration of the liquid crystal panel 4R for red component light, and shows the incident surface side of the diffracted light Lr2. Since the other color component light liquid crystal panels 4G and 4B have the same configuration as the red component light liquid crystal panel 4R, illustration and description thereof are omitted. The liquid crystal panel 4R has an irradiation area LA irradiated with the diffracted light Lr2 (FIG. 2). The irradiation area LA has a rectangular pixel area PA in which a plurality of rectangular pixels PX are arranged vertically and horizontally. In the drawing, a partial area EA (an area corresponding to 25 pixels of 5 pixels in the vertical direction and 5 pixels in the horizontal direction) including any 25 pixels in the pixel area PA is shown in an enlarged manner. Each pixel PX modulates incident light based on a modulation signal (also referred to as a “drive signal”) described later.

FIG. 4 is a schematic diagram illustrating an internal configuration of the image display apparatus 100. The image display device 100 includes an image signal generation unit 40, a modulation signal generation unit 50, and a random noise signal generation unit 60. The image signal generation unit 40 transmits a moving image signal VS representing a moving image to the modulation signal generation unit 50. The moving image signal VS is a digital signal including a frame image signal FS _n representing a frame image F _n that is updated at a constant frame period. Note that the subscript n of the frame image F _n is a natural number and indicates the display order of each frame image.

When receiving the moving image signal VS, the modulation signal generation unit 50 starts generating a drive signal MS (modulation signal MS) for controlling the modulation operation of the liquid crystal panels 4R, 4G, and 4B for each color component light. Specifically, the modulation signal generation unit 50 sequentially generates the frame image modulation signal FM _n for reproducing each frame image F _n every time it receives each frame image signal FS _n included in the moving image signal VS. To do. Further, every time the frame image modulation signal FM _n is generated, the modulation signal generation unit 50 issues a transmission request for the random noise signal RNS _m to the random noise signal generation unit 50.

The random noise signal generation unit 60 modulates a random noise signal RNS _m representing a noise image RN _m having a random noise pattern (hereinafter referred to as “random noise image RN _m ”) in response to a request from the modulation signal generation unit 50. It transmits to the signal generation part 50. Here, “random noise pattern” means that when a display image obtained by continuously displaying a plurality of noise patterns in time is integrated in the time direction, a substantially uniform image in which a specific pattern does not appear is obtained. This means a noise pattern that can be obtained. Note that the subscript m of the random noise image RN _m and the random noise signal RNS _m is a natural number and represents the order of transmission to the modulation signal generation unit 50.

Figure 5 is a schematic diagram showing a specific example of the random noise image RN _m, similarly to the pixel area PA in FIG. 3 shows an enlarged part area EA of the random noise image RN _m. In the random noise image RN _m , a noise pattern is configured by randomly distributing translucent pixels PXp that substantially transmit light and light-shielding pixels PXs that substantially block light. Note that the random noise image RN _m may be generated by the random noise signal generation unit 60, or may be stored in advance in a storage unit (not shown) of the image display device 100.

By the way, in this specification, the ratio of the number of translucent pixels PXp to the total number of pixels of the random noise image RN _m is referred to as “aperture ratio”. In this embodiment, a random noise image RN _m having an aperture ratio of about 80% is used. The reason for this will be described later.

When receiving the random noise signal RNS _m , the modulation signal generation unit 50 (FIG. 4) generates a random noise modulation signal RNM _m for reproducing the random noise image RN _m . Modulation signal generator 50, the random noise modulation signal RNM _m each liquid crystal panel 4R as the modulation signal MS continues after the frame image modulation signal FM _n, transmits 4G, to 4B. The modulation signal MS generated by the modulation signal generation unit 50 is a signal in which the frame image modulation signal FM _n and the random noise modulation signal RNM _m are alternately generated.

FIG. 6 is an explanatory diagram showing an example of a timing chart of the modulation signal MS. The modulation signal generation unit 50 adjusts the display time of the frame image modulation signal FM _n and the random noise modulation signal RNM _m so that the period of the update timing of the frame image F _n is maintained at a constant frame period. “Update timing” means the display start time of a new display image. In this embodiment, the image display periods of the frame image modulation signal FM _n and the random noise modulation signal RNM _m are both approximately 1/120 seconds, and the cycle of the update timing of the frame image F _n is the frame cycle in the moving image signal VS. Is held at 1/60 second.

FIG. 7 is a schematic diagram in which display images projected on the projection screen 200 are arranged in time series as a result of the liquid crystal panels 4R, 4G, and 4B for color component light performing the modulation operation according to the modulation signal MS. As described above, the frame image F _n and the random noise image RN _m are alternately updated and displayed about every 1/120 second in accordance with the modulation signal MS (FIG. 6).

By the way, when laser light is used as a light source as in the image display apparatus 100, since the laser light has high coherence (coherence), when it is diffused by an optical element arranged in the optical path, a random interference pattern (spec) Lupatan) may occur. When the speckle pattern occurs, the viewer of the display image may feel a flickering feeling on the display image and may recognize that the display image is unclear. However, as in the present embodiment, even when speckle patterns occur due to the random noise image RN _m being intermittently inserted between the frame images F _n constituting the moving image, the display image Can be prevented from recognizing the influence of the speckle pattern on the display image. The reason for this will be described below.

FIG. 8 is a schematic diagram showing the optical paths of the laser beams of the respective color components of the image display device 100 as one linear optical path LP for convenience. In FIG. 8, illustration of the cross dichroic prism 20 (FIG. 1) and the field lens 3 (FIG. 2) is omitted. For the sake of convenience, the projection screen 200 and the display images F _n and RN _n are shown separately.

Laser light emitted from the laser array light source devices 1R, 1G, and 1B is diffused and modulated via the diffractive optical element 2, the liquid crystal panels 4R, 4G, and 4B, and the projection lens 30, and then to the projection screen 200. And is viewed by the observer 300 as display images F _n and RN _n . Here, the complex amplitude of light in the pixel area PA of the liquid crystal panels 4R, 4G, 4B at time t is A (x, y) _t . The transfer function of the projection lens 30 is L (x, y). In addition, x and y show the coordinate in an image, respectively (arrow in a figure). At this time, the complex amplitude I (x, y) _t of the display images F _n and RN _{m on} the projection screen 200 at time t is expressed by the following equation (1). The symbol “*” indicates a convolution integral.
I (x, y) _t = L (x, y) * A (x, y) _t (1)
From equation (1), the light intensity O (x, y) _t of the image recognized by the observer 300 at time t can be obtained as the square of the absolute value of the complex amplitude I (x, y) _t (next) Formula (2)).
O (x, y) _t = | I (x, y) _t | ² (2)

Incidentally, the image display apparatus 100, a frame image F _n and the random noise image RN _m is gradually displayed in the period of the alternating 1/120 seconds. When the image is updated over time as described above, the light intensity O (x, y) of the image recognized by the observer 300 within a predetermined time is set to the light intensity O (x, y) _t . It can be obtained approximately by integrating in the time direction. The following equation (3) shows the integration result. Note that t1 to tk (k is a natural number) indicate the update time of the image.
O (x, y) = O (x, y) _t1 + O (x, y) _t2 +... + O (x, y) _tk (3)

FIG. 9 is a graph for explaining the effect of suppressing speckle patterns by inserting a random noise image into a moving image. Each graph G1, G2, G3 shows the light intensity distribution in the X-axis direction (FIG. 8) of the projection screen. Here, it is assumed that all the frame images F _n displayed on the image display device 100 are all white images. The first graph G1 shows the light intensity distribution of the frame image F ₁ displayed first. An all-white display image should originally have a substantially uniform light intensity distribution. However, the generation of speckle patterns causes a non-uniform light intensity distribution as shown in the first graph G1. Yes. In the subsequent frame images F _{2 to} F _n , the same light intensity distribution as that in the first graph G1 is shown.

The second graph G2 shows the light intensity distribution of the random noise image RN ₁ displayed next to the frame image F ₁ . In the random noise image RN ₁ , a random light intensity distribution different from that in the frame image F ₁ is obtained according to the displayed random noise pattern. In addition, in the random noise images RN _{2 to} RN _m displayed subsequently, the light intensity distribution corresponding to each random noise pattern is shown.

That is, in the image display apparatus 100 of the present embodiment, when the image is displayed, the random noise image RN _m is inserted, so that the light intensity distribution on the projection screen 200 changes randomly at a period of 1/120 second. Will be. This means that the complex amplitude at the focal plane changes with time.

Here, the first and second graphs G1 and G2 can respectively correspond to the first term and the second term on the right side of the above equation (3). That is, t1 = 1/120 seconds, t2 = 2/120 seconds,..., Tk = 120/120 seconds, and the light intensity O (x, y) _t of the display images F _n and RN _{n at} the respective image update times is set. In addition, it is possible to approximately obtain the light intensity O (x, y) recognized by the observer 300 in about 1 second.

  The third graph G3 shows the light intensity distribution obtained as a result. Compared with the first graph G1, it can be confirmed that the non-uniformity of the light intensity distribution is reduced. That is, in this image display apparatus 100, the speckle pattern is temporally changed by temporally changing the complex amplitude in the focal plane of the laser light, and the observer of the display image recognizes the speckle pattern. Suppress.

In order for the observer of the display image to recognize that the motion represented in the moving image is smooth, it is preferable that 60 or more frame images are displayed in about the same period as the original frame period. . Therefore, the image display apparatus 100 holds the updating period of the frame image F _n constituting the moving constant at 1/60 second. Accordingly, the insertion of the random noise image does not hinder the recognition of the moving image by the viewer of the display image.

On the other hand, in order to prevent the observer from recognizing the random noise image RN _m , it is preferable to insert 60 or more random noise images each having a different noise pattern in about 1 second. However, the display period of the random noise image may be shorter than the display period of the frame image. Therefore, the timing chart of the modulation signal MS can be generalized as follows.

FIG. 10 is a diagram illustrating an example of a generalized timing chart of the modulation signal MS. FIG. 10 is substantially the same as FIG. 6 except that the variables t and u representing the image display period based on the frame image modulation signal FM _n and the random noise modulation signal RNM _m are used. The variable t is an arbitrary real number of 0.5 or more, and the variable u is an arbitrary real number of 60 or more. In this generalized modulation signal MS, the frame image modulation signal FM _n is transmitted at t / u seconds, and then the random noise modulation signal RNM _m is transmitted at (1-t) / u seconds. Thereby, the update cycle of the displayed frame image F _n is maintained at 1 / u second, and u different random noise images RN _m are displayed per second.

Incidentally, the aperture ratio of the random noise image RN _m corresponds to an average brightness of the entire random noise image RN _m. Therefore, the effective luminance of the display image changes according to the aperture ratio of the inserted random noise image RN _m and the display time thereof. Here, the “effective luminance of the display image” refers to the case where the random noise image RN _m is inserted with reference to the temporal average luminance of all the images when only the frame image F _n that is an all white image is displayed. It means relative average brightness.

When the effective luminance of the display image is set to be extremely low (for example, about 70%), the viewer of the display image feels that the display image is dark. On the other hand, when the effective luminance of the display image is set to be extremely high (for example, about 100%), the aperture ratio of the random noise image RN _m is also extremely high, and the effect of suppressing the influence of the speckle pattern on the display image is reduced. End up. Accordingly, the effective luminance of the display image is preferably appropriately maintained so that the temporal average of the luminance of the display image does not extremely decrease, and is preferably about 85% to about 95%, for example. In order to maintain such desirable effective luminance, the aperture ratio of the random noise image RN _m can be set by the following method.

Figure 11 is an explanatory diagram showing an example of a method for determining the aperture ratio of the random noise image RN _m. The effective luminance y of the display image when the modulation signal MS of FIG. 10 is transmitted can be expressed by the following equation (4).
y = t + x (1-t) (4)
Here, x is the aperture ratio of the random noise image RN _m , t is the display time ratio of the random noise image RN _{m to} the display time of all display images, and corresponds to t described in FIG.

Here, when the effective luminance y of the display image to be ensured in the image display device 100 is set to 90% and is substituted into the above equation (4) and the equation is modified, the following equation (5) is obtained.
x = (0.9-t) / (1-t) (5)
From this equation (5), the graph of FIG. 11 is obtained, and the aperture ratio x corresponding to the display time ratio t of the random noise image RN _m can be determined. For example, in the modulation signal MS described with reference to FIG. 6, since t = 0.5, the effective luminance of the display image is maintained at about 90% by setting the aperture ratio of the random noise image RN _m to about 80%. be able to.

By the way, as described above, in order to suppress the observer of the display image from recognizing the random noise image RN _m , all the noise patterns of the random noise image displayed for about 1 second should be different. preferable. Further, in order to set the maximum aperture ratio of the random noise image RN _m to 80%, the noise pattern should be configured at such a ratio that at least 5 light-shielding pixels PXs are distributed in a partial region including any 25 pixels. Good. There are 53130 (= ₂₅ C ₅ ) arrangement patterns of the light-shielding pixels PXs in a partial region including the arbitrary 25 pixels. Then, when the display image is updated at about 120 Hz as in this embodiment, there are about 60 random noise images RN _m inserted in about 1 second, so even if the aperture ratio is set to a maximum of 80%. can be all different patterns of random noise pattern of the random noise image RN _m displayed in approximately one second.

  As described above, according to the configuration of the present embodiment, even when speckle patterns are generated in the image light, the frame image and the noise image are alternately displayed so that the viewer of the display image can display the display image. Recognizing the influence of speckle patterns can be suppressed.

B. Second embodiment:
FIG. 12 is a schematic diagram showing an internal configuration of an image display apparatus 100A as a second embodiment of the present invention. 12 is substantially the same as FIG. 4 except that a modulation signal generation unit 50A having a luminance detection unit 52 is provided instead of the modulation signal generation unit 50. The other configuration of the image display device 100A is the same as that of the first embodiment (FIG. 1).

Brightness detection unit 52, whenever the modulation signal generator 50A receives the frame image signal FS _n of video signal VS from the image signal generating unit 40, the average of each of the frame images F _n represented by each frame image signal FS _n The brightness level is calculated. When the modulation signal generation unit 50A requests the random noise signal generation unit 60 to transmit the random noise signal RNS _m , the modulation signal generation unit 50A also transmits the average luminance level calculated together with the transmission request. The random noise signal generation unit 60 transmits the random noise signal RNS _m of the random noise image RN _m having an aperture ratio corresponding to the received average luminance level to the image signal generation unit 40.

Here, when the average luminance level of the frame image F _n preceding the random noise image RN _m is z, the aperture ratio x of the random noise image RN _m is determined according to the following equation (6), for example.
x = z · x ₀ (6)
Here, x ₀ is a preset fixed value (maximum aperture ratio). That is, the aperture ratio x of the random noise image RN _m can be determined by multiplying the average luminance level z of the preceding frame image F _n by the predetermined maximum aperture ratio x ₀ .

Incidentally, the characteristics shown in FIG. 11 described above can be considered to be characteristics when the average luminance level z of the preceding frame image F _n is 1.0 (100%). At this time, the aperture ratio x given by the characteristics of FIG. 11 corresponds to the maximum opening ratio x ₀ of the equation (6). Therefore, for example, when the frame image display period ratio t is 0.5, the maximum aperture ratio x ₀ is preferably set to 0.8.

13A and 13B are explanatory diagrams for explaining the setting of the aperture ratio of the random noise image RN _m according to the average luminance level of each frame image F _n . As described above, in the second embodiment, the maximum aperture ratio of the random noise image RN _m is 80%. Accordingly, when the frame image F _n is an all-white image (luminance level 100%), the aperture ratio x of the random noise image RN _m displayed subsequent to the frame image F _n is 80% of the maximum value ( FIG. 13 (A)). In FIG. 13A, an arbitrary partial area EA of the random noise image RN _m is shown enlarged. 25 pixels in the partially enlarged area EA include 5 light-shielding pixels PXs and 20 light-transmitting pixels PXp.

FIG. 13B is a diagram similar to FIG. 13A, in which a random noise image RN _m having an aperture ratio of about 48% is displayed following a frame image F _n having a luminance level of 60%. Is shown. That is, the random noise image RN _m displayed following the frame image F _n other than the all-white image has a random aperture ratio corresponding to a value obtained by multiplying the luminance level of the frame image F _{n by} the maximum aperture ratio of 80%. A noise image RN _m is displayed.

As described above, the aperture ratio of the random noise image RN _m is set in conjunction with the luminance level of the frame image F _n displayed immediately before, thereby rapidly increasing the luminance level of the display image by the random noise image RN _m. Change can be suppressed. Therefore, it is suppressed that the observer of the display image recognizes the deterioration of the display image.

C. Third embodiment:
FIG. 14 is a schematic diagram showing the internal configuration of an image display device 100B as a third embodiment of the present invention. FIG. 14 is substantially the same as FIG. 12 except that the modulation signal generation unit 50B includes the prediction frame generation unit 54 and the illustration of the image signal generation unit 40 and the random noise signal generation unit 60 is simplified. . The other configuration of the image display device 100B is the same as that of the second embodiment (FIG. 1).

When receiving the moving image signal VS from the image signal generation unit 40, the modulation signal generation unit 50 </ b> B passes it to the prediction frame generation unit 54. Whenever the frame image signal FS _{n + 1} included in the moving image signal VS is received, the predicted frame generation unit 54 is based on the frame image signal FS _n and the frame image signal FS _{n + 1} received immediately before that. generating a predicted frame image signal FSi _n representing the prediction frame image Fi _n Te.

Figure 15 is an explanatory diagram for specifically explaining the predicted frame image Fi _n. Each of the first and second frame images F ₁ and F ₂ is a continuous frame image representing a moving image representing a running vehicle. The position of the vehicle is different between the first and second frame images F ₁ and F ₂ . In this case, an image in which the vehicle is present at an intermediate position between the vehicle positions shown in the first and second frame images F ₁ and F ₂ is inserted as the predicted frame image Fi ₁ . Thereby, the observer of the display image can feel the movement represented by the moving image more smoothly. As a method of generating a predicted frame image Fi _n, it is possible to employ any method such as a method of predicting an intermediate position of the moving object using the motion vector of the moving object.

Prediction frame generator 54 (FIG. 14) transmits the predicted frame image signal FSi _n together with the frame image signal FS _n to luminance detector 52. Brightness detection unit 52, from the frame image signal FS _n and the predicted frame image signal FSi _n, the frame image F _n, each of which represents, and calculates an average luminance level of the entire image Fi _n, further the average luminance level of the images The average value is calculated.

Modulation signal generation unit 50B transmits a transmission request for random noise signal RNS _m to random noise signal generation unit 60 (FIG. 12) together with the average value. The random noise signal generation unit 60 transmits a random noise signal RNS _m representing the random noise image RN _m having an aperture ratio corresponding to the average value of the received average luminance levels to the modulation signal generation unit 50B. Here, by multiplying the maximum aperture ratio of the random noise image RN _m (about 80%) to determine the opening ratio of the random noise image RN _m to the average value of the second embodiment similarly to the average luminance level. However, as in the first embodiment, the aperture ratio of the random noise image RN _m may be constant.

Modulation signal generation unit 50B (FIG. 14), the frame image signal FS _n and the predicted frame image signal FSi _n generates a frame image modulation signal FM _n and the predicted frame image modulation signal FMi _n from the respective liquid crystal panels 4R as the modulation signal MS , 4G, 4B. In addition, the modulation signal generation unit 50B subsequently generates a random noise modulation signal RNM _m from the random noise signal RNS _m and transmits the random noise modulation signal RNM _m to the liquid crystal panels 4R, 4G, and 4B as the modulation signal MS.

FIG. 16 is a timing chart of the modulation signal MS transmitted to each liquid crystal panel 4R, 4G, 4B. Modulation signal generating unit 50B, as the update period of each frame image Fn is held in 1/60 seconds, the time display by the predicted frame image modulation signal FMi _n and the random noise modulation signal RNM _m is adjusted. Specifically, when the display time by the frame image modulation signal FM _n is t1 seconds, the display time by the predicted frame image modulation signal FM _n is t2 seconds, and the display time by the random noise modulation signal RNM _m is t3 seconds, The sum of the display times t1, t2, and t3 is set to be about 1/60 second. Incidentally, the predicted frame image Fi _n in this case is generated by predicting an image after t1 seconds from the display timing of each frame image F _n.

FIG. 17 is a schematic diagram schematically showing a display image displayed on the projection screen 200 (FIG. 1) in time series by the image display apparatus of the third embodiment. The projection screen 200, the first predicted frame image Fi ₁ in which the first and subsequent to the first frame image F ₁ generated from the second frame image F _1, F ₂ is displayed. Furthermore, after the random noise image RN ₁ is displayed, the second frame image F ₂ is displayed. Thereafter, similarly, the frame image F _n, the predicted frame image Fi _n, repeating images in the order of the random noise image RN _m is displayed is updated.

Here, for example, if the average luminance level of the first frame image F ₁ is about 48% and the average luminance level of the first predicted frame image Fi ₁ is about 52%, the two frame images F ₁ , The average value of the average brightness level of F ₂ is about 50%. Accordingly, the aperture ratio of the subsequently displayed random noise image RN ₁ is approximately 40%, which is obtained by multiplying the average value of the received average luminance levels by the maximum aperture ratio of approximately 80%. In the figure, the partial area EA including any 25 pixels of the random noise image RN ₁ is shown in an enlarged manner. However, the 25 pixels in the area EA include 10 translucent pixels PXp. Yes.

  As described above, according to the configuration of the third embodiment, even when a predicted frame image is inserted, the display of the speckle pattern recognized by the observer of the display image is performed as in the first to third embodiments. It is possible to reduce the influence on the image. In addition, even when multiple frame images are displayed in front of the random noise image, since the random noise image having an aperture ratio reflecting the luminance level of each frame image is inserted, the luminance of the display image A sudden change in level can be suppressed.

D. Fourth embodiment:
FIG. 18A is a schematic diagram showing a random noise image RN _m used in the fourth embodiment of the present invention. FIG. 18B shows a two-dimensional Fourier pattern FP obtained by spatial frequency analysis of the random noise image RN _m shown in FIG. In FIG. 18B, the vertical axis indicates the vertical frequency and the horizontal axis indicates the horizontal frequency, with the center of the image being 0 frequency. In addition, the white area indicates that the intensity at the corresponding frequency is large. The configuration of the image display apparatus in the fourth embodiment is the same as that of the third embodiment (FIGS. 1 and 14).

To the observer of the displayed image to reduce the influence on the display image of the recognized speckle pattern is by insertion of a random noise image RN _m, preferably be varied larger complex amplitude at the focal plane. In order to vary the complex amplitude more greatly, the random noise image RN _m preferably has a higher frequency component. That is, as in the two-dimensional Fourier pattern FP, it is preferable that the intensity of the outer peripheral region (high frequency band) is larger than the central region (low frequency band near 0 frequency). Note that the random noise image RN _m can be generated by performing an inverse Fourier transform on a two-dimensional Fourier pattern indicating a frequency intensity distribution such as the two-dimensional Fourier pattern FP.

As described above, in the image display apparatus according to the fourth embodiment, the random noise signal generation unit 60 (FIG. 12) generates the random noise signal RNS _m representing the random noise image RN _{m in} which the intensity of the high frequency component is larger than the low frequency component. It transmits to the modulation signal generation unit 50B. Therefore, the influence of the speckle pattern recognized by the viewer of the display image on the display image can be reduced.

E. Example 5:
FIG. 19A is a schematic diagram schematically showing an optical path of a laser beam of an image display device as a fifth embodiment of the present invention. 19 (A) is a point at which the aperture stop 31 is provided on the projection lens 30, except that the liquid crystal panel 4R, 4G, random noise image RN _m in the pixel area PA and the projection screen 200 of 4B are displayed Is substantially the same as FIG. The other configuration of the image display apparatus in the fifth embodiment is the same as that in the fourth embodiment (FIGS. 1 and 14).

The image light representing the random noise image RN _m has a two-dimensional Fourier pattern shown in FIG. 18B on the cross section of the plane parallel to the liquid crystal panels 4R, 4G, and 4B at the position of the aperture stop 31 of the projection lens 30. Appears. Thus, the opening 32 of the aperture stop 31 is preferably open so as not to shield the high-frequency components of the random noise image RN _m (wide-angle component). At this time, the outer periphery of the opening 32 of the aperture stop 31 substantially coincides with the outer periphery of the bright region in FIG.

FIG. 19B is a schematic diagram schematically showing an optical path of laser light of an image display device as a comparative example of the fifth embodiment. FIG. 19B is almost the same as FIG. 19A except that the aperture 32 of the aperture stop 31 is smaller than that of FIG. In the case of this comparative example, the high frequency component of the image light representing the random noise image RN _m is blocked by the aperture stop 31 and does not reach the projection screen 200. That is, the variation of the complex amplitude in the projection screen 200 due to the random noise image RN _m is reduced by the amount that the high frequency component of the random noise image RN _m is shielded. Therefore, the image display device of the comparative example has a greater influence on the display image due to the speckle pattern recognized by the viewer of the display image.

Thus, the aperture stop 31 of the projection lens 30 preferably has a size that does not shield the high frequency components of the random noise image RN _m. For example, the F value of the aperture stop 31 may be made smaller than 2.0. Thereby, the influence on the display image by the speckle pattern recognized by the observer of the display image can be further reduced.

F. Example 6:
FIG. 20 is a schematic diagram showing an internal configuration of an image display device 100E as a sixth embodiment of the present invention. FIG. 20 is substantially the same as FIG. 14 except that a modulation signal generation unit 50E is shown instead of the modulation signal generation unit 50B. The other configuration of the image display device 100E is the same as that of the fifth embodiment (FIG. 1).

The modulation signal generation unit 50E includes a noise image synthesis unit 56. Modulation signal generation unit 50E, every time it receives a frame image signal FS _n included from the image signal generating unit 40 to the video signal VS, issues a transmission request of a random noise signal RNS _m to random noise signal generator 60. The random noise signal generation unit 60 transmits a random noise signal RNS _m representing a different random noise image RN _m for each transmission request to the modulation signal generation unit 50E.

Modulation signal generator noise image synthesizing unit 56 of the 50E generates a random noise frame image signal RFS _n obtained by synthesizing the frame image signal FS _n and the random noise image RN _m. That is, the image represented by the random noise frame image signal RFS _n is an image in which random noise is inserted into the frame image F _n . Modulation signal generation unit 50E generates a random noise frame modulation signal RFM _n is the modulated signal on the basis of the random noise frame image signal RFS _n, and transmits the modulated signal MS to the liquid crystal panels 4R, 4G, 4B.

FIG. 21 is an explanatory diagram showing an example of a timing chart of the modulation signal MS in the sixth embodiment. Modulation signal generation unit 50E, as the frame period is held in 1/60 second, and transmits the random noise frame modulation signal RFM _n. As a result, the frame image on which the random noise pattern is superimposed is updated and displayed on the projection screen 200 (FIG. 1) every 1/60 seconds.

  Even with such a configuration, the complex amplitude in the focal plane can be changed by the change of the inserted random noise pattern, and it is possible to suppress the observer of the display image from recognizing the influence of the speckle pattern on the display image. If the frame period of the image is 1/60 second or less, it is possible to suppress the observer of the display image from recognizing noise in the frame image. Note that when a predicted frame image is generated as in the third embodiment, a noise image may be combined with the original frame image and the predicted frame image, respectively.

G. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

G1. Modification 1:
In the above embodiment, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced by hardware. For example, part of the function of the modulation signal generation unit 50 can be executed by the image signal generation unit 40 or the random noise signal generation unit 60.

G2. Modification 2:
In the above embodiment, the random noise signal generation unit 60 may generate a noise signal representing an image including noise that is not completely random, instead of the random noise signal RNS _m representing the random noise image RN _m .

G3. Modification 3:
In the above embodiment, a binary image is used as the random noise image RN _m , but the random noise image RN _m may be a multi-value image having a halftone. Further, a random noise image RN _m may be obtained by synthesizing different noise patterns for each color component. In these cases, the aperture ratio in the above embodiments may be interpreted as the average luminance level of the entire random noise image RN _m.

G4. Modification 4:
In the above embodiment, the random noise image RN _m is inserted for each display of each frame image F _n . However, if the display start cycle of each frame image F _n and the predicted frame image is kept substantially constant, It may be inserted periodically at a different period from the frame image F _n .

G5. Modification 5:
In the above embodiment, each of the image light emitting devices 10R, 10G, and 10B includes the liquid crystal panels 4R, 4G, and 4B (FIGS. 2 and 3), but instead of the liquid crystal panels 4R, 4G, and 4B, Digital Micromirror Other light modulation devices such as Device (trademark of Texas Instruments) may be provided.

G6. Modification 6:
In the second embodiment and the third embodiment, the aperture ratio of the random noise image RN _m is determined by multiplying the value of the luminance level received by the random noise signal generation unit 60 by the maximum aperture ratio. It may be determined by a method. The aperture ratio of the random noise image RN _m may be determined in conjunction with the luminance level random noise signal generator 60 has received.

G7. Modification 7:
In the third embodiment, the predicted frame image Fi _n has been generated and inserted only one frame, or as a further plurality of predictive frame picture is generated and inserted. Further, in the sixth embodiment, all the frame images F _n was replaced with the random noise frame images RF _n, assuming that only a part of the frame image F _n is replaced with the random noise frame images RF _n Also good.

Schematic which shows the structure of the image display apparatus in 1st Example. Schematic which shows the structure of the image light emission apparatus in 1st Example. Schematic which shows the structure of the liquid crystal panel in 1st Example. Schematic which shows the internal structure of the image display apparatus in 1st Example. Explanatory drawing for demonstrating a random noise image. Explanatory drawing which shows an example of the timing chart of the modulation signal in 1st Example. Explanatory drawing which shows the display image in 1st Example typically in time series. Explanatory drawing which shows typically the optical path of the laser beam in an image display apparatus. Explanatory drawing for demonstrating reduction of the influence on the display image of a speckle pattern. Explanatory drawing for demonstrating generalization of the timing chart of the modulation signal in 1st Example. Explanatory drawing for demonstrating the determination method of the maximum aperture ratio of the random noise image in 1st Example. Schematic which shows the internal structure of the image display apparatus in 2nd Example. Explanatory drawing for demonstrating the relationship between the average luminance level of the frame image in 2nd Example, and the aperture ratio of a random noise image. Schematic which shows the internal structure of the image display apparatus in 3rd Example. Explanatory drawing for demonstrating the production | generation of the prediction frame image in 3rd Example. Explanatory drawing which shows an example of the timing chart of the modulation signal in 3rd Example. Explanatory drawing which shows the display image in 3rd Example typically in time series. Explanatory drawing which shows the random noise image and its two-dimensional Fourier pattern in 4th Example. The schematic diagram which showed typically the optical path of the image display apparatus in 5th Example, and the schematic diagram which shows the comparative example. Schematic which shows the internal structure of the image display apparatus in 6th Example. Explanatory drawing which shows an example of the timing chart of the modulation signal in 6th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1R, 1G, 1B ... Laser array light source device 2 ... Diffractive optical element 3 ... Field lens 4R, 4G, 4B ... Liquid crystal panel 10R, 10G, 10B ... Image light emission device 20 ... Cross dichroic prism 21R, 21G, 21B ... Side 22 ... Ejection surface 30 ... Projection lens 31 ... Aperture stop 32 ... Aperture 40 ... Image signal generator 50 ... Random noise signal generator 50, 50A, 50B, 50E ... Modulation signal generator 52 ... Luminance detector 54 ... Prediction frame generation part 56 ... noise image synthesizing unit 60 ... random noise signal generating unit 100, 100A, 100B, 100E ... image display device 200 ... projection screen 300 ... observer EA ... partially enlarged region F _n ... frame image FM _n ... frame image modulation signal FMi _n ... predicted frame image modulation signal FS _n ... frame image signal FSi _n ... Prediction frame image signal F _n ... Prediction frame image G1, G2, G3 ... Graph LA ... Irradiation area LP ... Optical path Lr1 ... Laser beam Lr2 ... Diffracted light MS ... Modulation signal PA ... Pixel area PX ... Pixel PXp ... Translucent pixels PXs ... shielding pixel RF _n ... random noise frame image RFM _n ... random noise frame modulation signal RFS _n ... random noise frame image signal RN _m ... random noise image RNM _m ... random noise modulation signal RNS _m ... random noise signal VS ... video signal

Claims (11)

An image display device using a laser light source,
A light modulation unit that modulates laser light emitted from the laser light source into image light representing an image;
A drive signal generation unit that generates a drive signal for driving the light modulation unit based on an image signal of a frame image updated at a constant first period;
With
The image display device, wherein the drive signal generation unit periodically inserts a noise image into the drive signal while maintaining a timing at which display of the frame image is updated in the first cycle. The image display device according to claim 1,
The noise image periodically inserted is an image display device that is a random noise image that becomes a uniform image in which a specific pattern does not appear when a plurality of noise images are integrated in a time direction. The image display device according to claim 1 or 2,
The drive signal generator is
Generating a frame image drive signal for displaying the frame image as a non-noise frame image not including the noise image in the first period;
An image display device that generates a noise image drive signal for displaying the noise image at a constant second period. The image display device according to claim 3,
The drive signal generation unit further generates a predicted frame image predicted as an intermediate image between each pair of frame images arranged in chronological order as a non-noise frame image not including the noise image, and the predicted frame image An image display device that generates a predicted frame image drive signal for displaying the image at the first period. The image display device according to claim 3 or 4, wherein
The image display device, wherein the second period is equal to the first period. An image display device according to any one of claims 3 to 5,
The image display device, wherein the average luminance level of the noise image is set in conjunction with an average luminance level of a predetermined number of the non-noise frame images displayed before the noise image. The image display device according to any one of claims 1 to 6,
When the noise image is Fourier-transformed, the amplitude intensity of the first frequency band whose frequency is near 0 is lower than the amplitude intensity of the second frequency band on the higher frequency side than the first frequency band. An image display device that is an image. An image display device according to any one of claims 1 to 7,
An image display device in which the noise images displayed within at least one second are all different. The image display device according to claim 1 or 2,
The drive signal generator is
An image display device that generates a frame image drive signal with noise for displaying a frame image with noise obtained by synthesizing the noise image with the frame image at the first period. The image display device according to claim 9,
The drive signal generation unit further includes
Generating a predicted frame image that is predicted as an intermediate image between each pair of frame images arranged in chronological order;
While generating a prediction frame image with noise obtained by synthesizing the noise image with the prediction frame image,
The image display apparatus which produces | generates the prediction frame image drive signal with a noise for displaying the said prediction frame image with a noise with a said 1st period. An image display method for displaying a frame image on a display screen by modulating laser light,
An image display method comprising the step of modulating the laser beam so that a noise image is periodically displayed on the display screen while maintaining a timing at which the display of the frame image is updated in a constant first cycle. .

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